1. Field of the Invention
The present invention relates generally to arc lamps and, more particularly, to arc lamps of the type which have short-arc gaps and integral, internal reflectors.
2. Description of the Prior Art
It is well known to utilize lamps having short-arc gaps and integral internal reflectors to provide compact yet intense point sources of light. Such lamps are utilized for example, in medical and industrial endoscopes. Generally speaking, such lamps include a sealed chamber which contains a gas pressurized to several atmospheres, an anode and cathode mounted along the central axis of the chamber to define an arc gap, an integral concave reflector which collimates light generated at the arc gap, and a window at the mouth of the concave reflector to permit external transmission of the collimated light from the reflector. When utilizing direct current to power such lamps, it is known to operate the lamps in a pulsed, low current manner. During non-pulsed operation, a small current (known as the simmer current) is provided to the lamp until such time as the lamp is pulsed; then the current is increased to as much as one-hundred amperes, averag% peak. In one mode of operation, for example, the pulses are generated about one every 1.5 seconds and each pulse has a duration of about 100 milliseconds (i.e., one-tenth second), resulting in an energy flow across the short-arc gap of several hundred joules for the duration of the pulse with the average current being about one-hundred amperes. Typical voltages required for starting such lamps are approximately 12,000 volts.
It is also known in the art to utilize short-arc lamps which do not have integral internal reflectors but, instead, have external reflectors. Such lamps are typically filled with xenon at pressures of several atmospheres when the lamp is cold; during operation, gas pressure within the lamp may triple. Further, it is known to operate such lamps with either relatively high or relatively low current pulses. When operated with high currents and short duration pulses, such lamps with external reflectors can be characterized as flashlamps. A disadvantage of such flashlamps with external reflectors, especially reflectors made of aluminum, is that oxides invariably form on the reflector surface. Such oxides have been found to absorb short wave length light, such as ultraviolet light, and therefore, seriously degrade the spectral performance of the lamp when the lamps are operated with relatively high current pulses.